1. Field of the Invention
The present invention relates generally to knife gate valves for controlling material flow along a path. More particularly, the present invention concerns an adjustable lockout device configured to securely lock the valve in a desired condition, and an improved valve design for use with the adjustable lockout device.
2. Discussion of Prior Art
Those ordinarily skilled in the art will appreciate that it is often necessary to lock a flow control valve in a select condition. For example, actuation of the valve is undesirable when an operator is maintaining or otherwise working on the valve. It is particularly important to lock out a remotely controlled valve, wherein valve actuation might cause damage to the valve or injury to an unsuspecting worker while the valve is being maintained. It is also common to lock a flow control valve in a closed position during maintenance of the flow line downstream from the valve. That is to say, it is often undesirable to have material flow through the line during line maintenance, and the valve may consequently be locked in a closed position to prevent material flow beyond the valve so that the portion of the line downstream from the valve can be worked on without material flowing therethrough.
However, numerous problems are associated with conventional valve lockout designs. For example, the valve lockout device may fail to securely lock the valve against actuation, which is especially problematic when a powerful actuator is utilized to open and close the valve. A number of lockout devices are not tamperproof and consequently may be removed by unauthorized personnel or by workers having no knowledge that the valve should remain locked out. In addition, a number of conventional valves are not designed to be locked out, and the valve must consequently be retrofitted with structure for selectively locking out the valve. The lockout devices utilized with such valves often do not effectively prevent valve actuation and are difficult to use.
One particular valve design (a so-called "gate valve") includes a casing connected to the flow line, a valve plate shiftable relative to the casing between open and closed positions, an actuator including a linearly shiftable control member connected to the valve plate for effecting shifting of the plate, and a pair of yokes rigidly interconnecting the actuator and casing. Those ordinarily skilled in the art will appreciate that conventional gate valve designs are particularly problematic. It is believed that no gate valve has heretofore been originally designed to include a lock out device, thereby requiring the valve to be retrofitted when a lockout device is desired. Such a retrofit typically includes a rigid, elongated, metal bar and a pair of spaced apart, metal blocks fixed to one of the yokes (e.g., by welding). Each of the blocks is positioned along the yoke at a location that allows the bar to be disposed between the block and the control member to prevent shifting of the control member relative to the yoke. As is customary, the bar and blocks are designed to lock the valve in the open and closed conditions.
Beyond requiring the valve to be retrofitted, this traditional design presents numerous additional problems. For example, a retrofitted valve is often incapable of being locked in a completely open and/or closed position. It is virtually impossible to precisely retrofit the valve, and consequently, there is often "slop" in the components used to lockout device. This will sometimes require removal and reinstallation of the retrofit components (e.g., when the bar is too large to be wedged between one of the blocks and the control member) or, in the alternative, slight shifting of the control member out of the open or closed conditions before the bar engages both the member and block in a manner to prevent further movement of the member. In the latter case, use of the lockout device may require a worker to hold the bar between one of the blocks and the control member as the member is shifted slightly from the selected lock out condition (e.g., open or closed). In addition, if the control member is subsequently shifted toward the select condition, the bar is likely to sufficiently disengage the control member and/or corresponding block and fall from its operating orientation. Furthermore, material will likely be permitted to flow through the valve if the valve plate is required to be shifted slightly out of the closed position. It has also been determined that most valves have a seat that will wear, and the location of the valve plate in the closed position will consequently change over time. Thus, even if the valve assembly were to be precisely retrofitted, the lockout device would eventually be incapable of locking the valve in the completely closed condition. This problem would be experienced even if the valve were to be precisely designed for use with the bar-type lockout device.